1. Field of Invention
The present invention pertains generally to retaining walls and more specifically to retaining walls using rigid tieback elements.
2. Description of the Background
Various retaining wall systems have been used in the prior art for retaining soil, i.e., loam, sand, dirt or any other type of earthen material. One broad classification of retaining wall systems is the stabilized earth system which generates a stabilized earth mass behind the retaining wall to reduce the likelihood of failure of the retaining wall. Typical techniques include the use of graded backfill and flexible tieback elements which help to form the stabilized earth mass.
Another broad classification of retaining wall systems is the static, leverage wall system, such as disclosed in U.S. Pat. No. 4,050,254 issued Sept. 27, 1977 to Meheen, et al. Design analysis of such static, leverage wall systems is accomplished by summing the forces on the rigid horizontal tieback element and comparing them with the horizontal component of soil forces acting on the face of the wall. The horizontal tieback base is then increased in size and length until the vertical forces on the tieback element exceed the horizontal component of the soil forces by a predetermined factor of safety. In other words, the leverage wall systems use a standard statics approach to analyzing the wall and sum the forces to provide a factor of safety which ensures that the overturning moments do not exceed the horizontal forces on the tieback elements by a predetermined factor of safety. This results in retaining walls having extremely long tieback elements, such as disclosed in Meheen et al., which require a large cut into the backfill material to erect the wall, or walls which have extremely large and heavy base portions, such as conventional, poured in place, cantilevered walls. Consequently, static leverage wall systems have not been suitable for implementation as high vertical walls because of the required cut into the backfill, or the large expense of constructing poured-in-place cantilevered walls which are expensive to pour and require an extremely large amount of concrete. Also, because of the unsuitability of leverage wall systems as high vertical walls, e.g. over 20 feet, they have generally been implemented as tiered walls with each successively higher tier set back into retained soil, ( such as disclosed in Meheen et al. U.S. Pat. No. 4,050,254 issued to Meheen et al. on Sept. 27, 1977 is specifically incorporated herein by reference and made a part of this document for all that it discloses.
U.S. Patent Application Ser. No. 773,328 filed Sept. 6, 1985 by Babcock et al. entitled "Retaining Wall System Using Soil Arching" discloses a multitiered retaining wall system which employs soil arching to produce a substantially vertical wall having a series of vertical tiers which individually articulate. The Babcock et al. application discloses a multitiered wall wherein each tier acts independently of other tiers (articulates) and generates shears and soil arching over each of the footings which extend into the soil to maintain the stability of the wall. The face of the wall system disclosed in the Babcock et al. application, referred to above, has a "shiplap" design and each of the column portions of the tieback elements protrudes by a predetermined distance from the face of the retaining wall panels. In certain instances, such as when a wall is installed adjacent a roadway, it is desirable to have a smooth faced wall without vertical column portions projecting from the wall to reduce the likelihood of contacting the vertically aligned projection with a motor vehicle. Consequently, it is desirable, in certain instances to provide a retaining wall which does not have vertically aligned projections.
Additionally, when using prefabricated concrete components in a retaining wall, it is desirable to use standardized pieces to reduce costs in the fabrication process. However, geotechnical conditions necessitate variations in the height of each tier of the retaining wall as well as the spacing between the tieback elements. Either different size elements must be fabricated, which increases the cost of fabrication due to additional costs for forms and other factors, or the wall must be designed for the most stringent design requirements, which results in a failure to optimize the design criteria of the retaining wall system. Consequently, some flexibility is desirable in the implementation of the retaining wall system to provide optimum design parameters which result in cost savings.